It is well known for lubricating oils to contain a number of surface active additives (including antiwear agents, dispersants, or detergents) used to protect internal combustion engines from corrosion, wear, soot deposits and acid build up. Often, such surface active additives can have harmful effects on engine component wear (in both iron and aluminum based components), bearing corrosion or fuel economy. A common antiwear additive for engine lubricating oils is zinc dialkyldithiophosphate (ZDDP). It is believed that ZDDP antiwear additives protect the engine by forming a protective film on metal surfaces. ZDDP may also have a detrimental impact on fuel economy and efficiency and copper corrosion. Consequently, engine lubricants may also contain a friction modifier to obviate the detrimental impact of ZDDP on fuel economy and corrosion inhibitors to obviate the detrimental impact that ZDDP may have on copper corrosion. Friction modifiers and other additives may also increase lead corrosion.
Further, engine lubricants containing phosphorus and sulfur compounds such as ZDDP have been shown to contribute in part to particulate emissions and emissions of other pollutants. In addition, sulfur and phosphorus tend to poison the catalysts used in catalytic converters, resulting in a reduction in performance of said catalysts.
There has been a commercial trend for reduction in emissions (typically reduction of NOx formation, SOx formation) and a reduction in sulfated ash in engine oil lubricants. Consequently, the amounts of phosphorus-containing antiwear agents such as ZDDP, overbased detergents such as calcium or magnesium sulfonates and phenates have been reduced. As a consequence, ashless additives have been contemplated to provide friction, antiwear, or antioxidant performance. It is known that surface active ashless compounds such as ashless friction modifiers may in some instances increase corrosion of metal, namely, copper or lead. Copper and lead corrosion may be from bearings and other metal engine components derived from alloys using copper or lead. Consequently, there may be a need to reduce the amount of corrosion caused by ashless additives.
U.S. Pat. No. 3,245,909 discloses lubricating compositions comprising a major amount of lubricating oil and minor amounts of an alkenyl succinimide dispersant and 2,4-dihydroxybenzoic acid.
U.S. Pat. Nos. 4,156,655 and 4,376,060 disclose lithium grease compositions made with boric acid, fatty acid and optionally a hydroxycarboxylic acid, including 2,5-dihydroxybenzoic acid (gentisic acid); 2,6-dihydroxybenzoic acid (gamma resorcyclic acid); and 4-hydroxy-4-methoxybenzoic acid.
U.S. Pat. No. 4,627,928 discloses basic magnesium salts of substituted aromatic hydroxy-containing carboxylic acids including alkyl-substituted 2,5-dihydroxy benzoic acid and alkylated 4,6-dihydroxy toluic acid.
U.S. Pat. No. 5,143,635 discloses a method of reducing drag in conduits by using an additive composition comprising a quaternary ammonium salt of 2,6-dihydroxybenzoic acid.
U.S. Pat. No. 5,686,398 discloses fuel and lubricant additives comprising aryl esters of hydroxyaromatic carboxylic acids, including dihydroxybenzoic acid and dihydroxynaphthoic acid.
U.S. Pat. No. 6,399,549 discloses cyclic coupling products of alkylphenols and at least one hydroxy-substituted aromatic carboxylic acid, which may optionally be selected from 2,4-dihydroxybenzoic acid, 3,5-dihydroxybenzoic acid, 2,5-dihydroxybenzoic acid, and/or 2,6-dihydroxybenzoic acid.
U.S. Pat. No. 5,576,274 discloses fuel and lubricant additives useful as dispersants and multifunctional viscosity modifiers wherein a dihydroxyaromatic compound is alkylated with an olefinic polymer and then aminated in such a manner as to oxidize the hydroxyl moieties of the dihydroxyaromatic compound to carbonyl groups.